Detector

One of the NOTCam detector quadrants failed. All the external wiring and associated boards in the controller were checked, but nothing could be found. The pre-amplifiers, mounted in small die-cast boxes on the side of the NOTCam vessel, where examined and amplifiers swapped but still the problem persisted. Then the amplifier boxes where physically removed, exposing the electrical connections of the detector, but as before nothing could be seen wrong. The boxes where remounted and magically the quadrant started working! It is believed that the probable cause of the fault was liquid nitrogen spilling from the filling tube which is directly above these amplifier boxes and associated vacuum connectors. A cardboard cover was made to protect the amplifiers from further LN2 spillage.

The "reset level" is the count level of the pre-integration readout of the array. It is supposed to be a function of detector temperature. When commissioning the array, it was adjusted to an optimal level, i.e. a level that maximises the dynamical range and minimises bad pixels. Over the years we have experienced various jumps in this level, needing a re-adjustment of the dc-offset voltages each time.

It was found that having the detector controller always switched on we no longer saw large jumps. However, recently large jumps have happened again and therefore the voltages needed to be adjusted. The monitoring of the reset-level has been restarted.